In drilling oil wells, it is sometimes necessary to install a downhole motor. Ordinarily, the motor force for the drilling operation is supplied by equipment at the well head comprising a rotary table and a prime mover connected to the rotary table for imparting rotation to the drill string. Sometimes, it is necessary to operate in a different fashion. As an example, it is sometimes necessary to sidetrack a hole. This is often done by installing a small motor at the bottom of the drill string, just above the drill bit and power the drill bit with a small motor.
The present invention is an improved downhole motor. Many motors have been devised, and it is believed that they are lacking. The present invention overcomes some of these drawbacks by providing a motor which delivers adequate power. Moreover, it is a ruggedized, sealed unit capable of handling very substantial stress. The working environment of the downhole drill bit is quite extreme. That is to say, the drill bit is subjected to high temperatures, sometimes extremely high pressure, and a tremendous amount of vibration. The present invention is a downhole motor which can accommodate the tough environment and yet function for substantial periods of time. Part of this results from the fact that the motor utilizes the drilling mud as a motive means and yet does not induce drilling mud into the motor itself. Drilling mud is the lubricant customarily pumped down the drill string for lubricating the drill bit. It serves other purposes including packing the sidewall of the open hole to prevent lateral leakage. For this reason, drilling mud is a rather heavy fluid made of abrasive materials including, but not limited to, various clays, etc. While the precise composition of drilling mud is not important to the present invention, it is worth observation to note that drilling mud is highly abrasive. The abrasive material is very hard on the working parts of the downhole motor. To this end, motors known heretofore have suffered great damage as a result of the flow of abrasive mud through the equipment.
The present invention does not induce drilling mud into it. More accurately, it has a closed circuit hydraulic system. The hydraulic system is actuated by mud pressure, but the mud is maintained in a controlled channel. More importantly, pressure variations in the mud pressure are used, not the flow of mud itself. This enables the equipment to last much longer.